Your painting looks great! When I painted mine I was somehow able to match the colors I wanted (I used an "over-exposed" board for reference) surprisingly well and I really can't say how... It just kind of happened. It just seemed so easy to paint and I believe you are discovering the same.
My project starts here:
http://forum.yeoldeinn.com/viewtopic.php?f=58&t=4254&hilit=whitebeard+projects&start=60#p88130There are a few tricks I would recommend:
(1) Paint black (like you are already doing) then dry brush white as a first step to help highlight the top most bits (see my works in progress). This undercoat gradient shows through thin layers of paint and looks fantastic.
(2) Paint the room with an exaggerated bright version of the color you want. This should still capture the gradients in the manner you have already done.
(3) Mix up your own BLACK and BLACK/BROWN washes (50% paint, 50% water, and a tiny bit of soap to break surface tension (I just used hand soap) and just brush it over the whole thing to darken and bring back any deep details which may have lost definition. You can even use the black wash in 3-5 applications to re-create the shadows near the walls.
(4) after the wash is dry, go back with the exaggerated color (colors) and add random highlights
Again, this is looking really great!
Has resigned from the forum and would delete his account if he could.